In the UMTS (Universal Mobile Telecommunications System) network, the specifications of long term evolution (LTE) have been drafted for the purpose of further increasing high speed data rates, providing lower delay and so on (see non-patent literature 1). In LTE, as multiple access schemes, a scheme that is based on OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlink channels (downlink), and a scheme that is based on SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in uplink channels (uplink). Also, successor systems of LTE (referred to as, for example, “LTE-advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) are under study for the purpose of achieving further broadbandization and increased speed beyond LTE, and the specifications thereof have been drafted (Rel. 10/11).
As duplex modes for radio communication in the LTE and LTE-A systems, there are frequency division duplex (FDD) to divide frequencies between the uplink (UL) and the downlink (DL), and time division duplex (TDD) to divide time between the uplink and the downlink (see FIG. 1A). In TDD, the same frequency region is applied to uplink and downlink communication, and signals are transmitted and received to and from one transmitting/receiving point by dividing time between the uplink and the downlink.
Furthermore, the half-duplex FDD scheme is another duplex mode. The half-duplex FDD scheme is a communication scheme which, similar to the FDD scheme, allocates different frequency regions between the uplink and the downlink, and which does not carry out uplink communication and downlink communication at the same time with respect to a given user terminal. That is, uplink communication and downlink communication with respect to a given user terminal are separated based on time. This separation of uplink communication and downlink communication based on time is shared in common with the TDD scheme operation.
Also, the system band of the LTE-A system (Rel. 10/11) includes at least one component carrier (CC), where the system band of the LTE system constitutes one unit. Gathering a plurality of component carriers (cells) to achieve a wide band is referred to as “carrier aggregation” (CA).